IRQ
Short for Interrupt ReQuest and pronounced as I-R-Q, IRQ is a signal that has a direct line to the computer processor allowing it to stop the processor momentarily and decide what to do next. IBM compatible computers go up to IRQ 15, and are prioritized in the computer according to the importance of the device. Today, most users will never nee to worry about IRQ settings because all devices are now PnP.
Tip: Technically there are 16 IRQs if you count IRQ 0, the system timer.
Also see: DMA, Hardware conflict, I/O port, Interrupts, IRQL